| | Affton, MO | Seaside, OR | United States |
| Population | 18,925 | 7,058 | 329,725,481 |
| Female Population | 49.0% | 55.4% | 50.5% |
| Male Population | 51.0% | 44.6% | 49.5% |
| Median Age | 42.5 | 51.2 | 38.4 |
| space3 | | | |
| Population - 2010 | 20,115 | 6,497 | 309,327,143 |
| Population - 2000 | 20,535 | 5,900 | 285,036,114 |
| Population - 1990 | 21,106 | 5,359 | 251,960,433 |
| Pop. 2000 to Now | 4.9% | 17.4% | 15.6% |
| Pop. 1990 to Now | 2.1% | 29.2% | 30.8% |
| space4 | | | |
| Population Density | 4,150.2 | 1,810.7 | 93.4 |
| Land Area | 4.6 | 3.9 | 3,531,905.4 |
| Water Area | 0.0 | 0.2 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Affton, MO | Seaside, OR | United States |
| Age 0 to 4 | 4.9% | 1.8% | 5.9% |
| Age 5 to 9 | 6.0% | 4.5% | 6.1% |
| Age 10 to 14 | 3.7% | 6.8% | 6.6% |
| Age 15 to 17 | 2.5% | 1.5% | 3.9% |
| Age 18 to 20 | 2.4% | 3.8% | 4.0% |
| Age 21 to 24 | 6.0% | 4.0% | 5.2% |
| Age 25 to 34 | 14.5% | 10.0% | 13.8% |
| Age 35 to 44 | 14.5% | 10.6% | 12.9% |
| Age 45 to 54 | 12.1% | 13.8% | 12.6% |
| Age 55 to 59 | 7.3% | 7.1% | 6.7% |
| Age 60 to 64 | 7.6% | 7.3% | 6.3% |
| Age 65 to 74 | 10.5% | 17.5% | 9.6% |
| Age 75 to 84 | 4.7% | 7.6% | 4.5% |
| Age 85 and over | 3.5% | 3.6% | 1.9% |
| space1 | | | |
| Race | | | |
| | Affton, MO | Seaside, OR | United States |
| White | 87.4% | 89.3% | 59.4% |
| Black | 2.8% | 2.6% | 12.2% |
| Asian | 2.3% | 1.2% | 5.6% |
| Native American | 0.1% | 0.9% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 4.0% | 0.1% | 3.2% |
| Hispanic | 3.4% | 5.9% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Affton, MO | Seaside, OR | United States |
| Married Population | 51.4% | 42.2% | 49.8% |
| Currently Married | 50.7% | 41.1% | 48.0% |
| Married but Separated | 0.7% | 1.1% | 1.8% |
| Single Population | 48.6% | 57.8% | 50.2% |
| Never Married | 29.3% | 25.8% | 33.8% |
| Divorced | 13.7% | 24.1% | 10.8% |
| Widowed | 5.6% | 7.9% | 5.6% |
| space5 | | | |
| Household Size | 2.20 | 2.03 | 2.60 |
| Households | 8,612 | 3,441 | 124,010,992 |
| Family Households | 4,837 | 1,496 | 80,755,759 |
| Married couple, w/children | 28.4% | 24.7% | 30.5% |
| Married couple, no children | 50.3% | 51.1% | 42.9% |
| Non Family Households | 3,775 | 1,945 | 43,255,233 |
| Single householder, w/children | 10.8% | 9.2% | 15.8% |
| Single householder, no children | 10.5% | 15.0% | 10.8% |